1. Field of the Invention
The present invention relates to a method for ablating a target object with a laser beam and an apparatus for such ablation.
2. Description of Related Art
A laser beam is used in various fields for medical treatment or processing. For example, in the ophthalmic field, there have been known laser apparatuses for ablating a cornea with a laser beam to change its corneal curvature so that a refractive error of an eye may be corrected. In this type of apparatus, an ablation rate (an ablation depth) per one shot of laser beams (or per one scan) often changes due to factors including laser output and changes in an irradiating optical system (a beam directing optical system). Therefore, it is important to ablate a target object such as a cornea in consideration of the change of the ablation rate.
The present applicant suggested a method for adapting to the change of the ablation rate in Japanese Patent Application Unexamined Publication No. Hei 06-226471 which corresponds to U.S. Pat. No. 5,624,436. The method consists of performing laser irradiation to ablate a surface of a transparent plate (a PMMA plate) having a known ablation rate so that the ablated surface may have a curved surface shape and intended refractive power, measuring with a lens meter or the like the refractive power of the curved surface of the transparent plate formed by the ablation, and correcting data for intended ablation based on a result of the measurement.
Such a method has provided a way to ablate a target object in consideration of the change of the ablation rate. Meanwhile, further techniques for more accurate ablation have been explored.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a method for easily evaluating ablation conditions and accurately ablating a target object, as well as an apparatus for such ablation.